major updates

This pull request is quite big and carries the following changes:

* syntax cleanup of all the B3 modules
* added deprecated decorator: mark a callable as deprecated
* make use of the new event handler system in all the plugins
* produce missing EVT_CLIENT_KICK in parsers
* general fixes in plugins and parsers
* added test cases for command !pluginfo and updated test cases to comply with the new changes

Separate note for the XLRstats:

* syntax cleanup
* make use of the new getCmd function defined in b3.functions
* make use of self.getEventID() to retrieve events ids
* make use of the new event handler system in XLRstatsPlugin
* make use of the new event handler system in CtimePlugin
* make use of the new event handler system in BattlestatsPlugin
* added debug information on plugin configuration file loading
* correctly declare Kfactor attribute in PlayerStats class
* replaced variables names using python built-in keywords
* match also 'yes' and 'no' keywords in !xlrhide command
* added missing call to super constructor in XlrstatshistoryPlugin
* added missing call to super constructor in CtimePlugin
* added missing call to super constructor in BattlestatsPlugin